Reciprocating pumps are frequently used in a variety of industrial applications for pumping liquids from storage containers. For example, pneumatic piston pumps are often used for pumping liquids from drums, barrels, plastic containers, or the like. In many applications, it is undesirable to allow the pumps to run dry for any significant length of time. For instance, unless an out-of-fluid condition is detected and the downstream process or operation employing the pumped liquid is interrupted, faulty downstream operations will be performed, or the downstream operations will be rendered impossible, because the required liquid will not be supplied. Thus, it is desirable to detect an out-of-fluid condition so that the pumps may be stopped as soon as possible and the pump connected to a new liquid supply to continue the downstream operations.
U.S. Pat. No. 4,269,223 discloses a detector for detecting an out-of-fluid condition in an air pump by sensing an increased rate of air flow to the pump which occurs when the pump runs dry. The device is installed in the line that supplies pressurized air to the air pump. The device shuts off the air flow when the increased air flow is detected. A disadvantage of the device is that if the air supply pressure to the pump changes, the device must be adjusted or it will either close prematurely or fail to close at all.